Recently, rotating devices move toward smaller size, and energy capacity gradually increases. Accordingly, the rotational speed of the main axis gradually increases, and the importance of high speed rotating element bearings gradually increases. Additionally, thus various types of bearings are applied to rotating devices, and among them, a ball bearing is one of the most widely used bearings. A general ball bearing includes an inner ring, an outer ring, and a cage that maintains a gap between balls.
A high speed ball bearing generally rotates by an interference fit between the inner ring and the main shaft, and with rotating and revolving motions of ball bearing elements, the cage also rotates in proportion to the speed of the inner ring. Particularly, in the case of a high speed rotating device, its rotational speed generally has number of DN 1,000,000 (rotary axis diameter (mm)*rpm) or more, and accordingly, the rotational speed of the cage also has number of about DN 400,000 or more. Equation (1) is a mathematical expression of the number of rotations of the cage upon rotation of the inner ring.
Equation (1) is
      cage    ⁢                  ⁢    whirling    ⁢                  ⁢    frequency    =      0.5    ×    r    ⁢                  ⁢    p    ⁢                  ⁢    m    ×          (              1        -                  D          dm                    )        ×          cos      ⁡              (        α        )            where rpm denotes the rotor rotating speed (inner ring), D denotes the ball diameter, dm denotes the averaging orbital diameter, and a denotes the contact angle.
Accordingly, in the high speed ball bearing, not only a dynamic relationship of the inner and outer rings and the balls but also as rotational stability of the cage has a great role in the overall stability of the ball bearing. FIG. 1 shows the causes of cage instability, and represents mechanism of intermittent collisions between the cage and the rolling elements. By these causes, the cage has intermittently abnormal whirling motions and number of whirling rotations, and referring to FIGS. 2A, 2B, 2C, 2D, 2E and 3A, the whirling scale and the whirling ratio of the cage during instability are depicted. As described above, the cage plays an important role for stable operation of the ball bearing, but research and development of the cage structure that can directly respond to this is still challenging.
To overcome this problem, methods for making the cage pocket design more flexibly have been primarily used, but this is a method that adjusts the structural stiffness of the cage, but not a method using a rotary force.
However, this method has a high likelihood that the strength of the cage itself reduces, causing damage of the cage, and its shape is complex, making it difficult to manufacture, resulting in a drastic increase in manufacturing costs, which limits the range of applications.